Sensors detecting species in fluids (gas or liquids) have become increasingly important in recent years. Solid-state fluid sensors are particular valuable because of their small size and mechanical robustness.
The ability to detect a small quantity of a species in a fluid with a solid-state sensor relies on having a large surface area where the fluid can interact with the sensor. Detection often relies on sensing a property such as a change in resistance, so the volume of the sensing element should be reduced as much as feasible to increase the surface to volume ratio; e.g., the fraction of the volume that is affected by surface changes.
Forming a large number of small sensing elements that can act in parallel is thus advantageous for providing a large signal, but using lithography to define the elements can be expensive. A technique that does not use fine-scale lithography or patterning techniques is advantageous. Making contact without detailed patterning is also important.